1. Field of the Invention
The present invention relates to a light emitting diode (LED), and relates more particularly to a lateral thermal dissipation LED.
2. Description of the Related Art
LEDs are currently used in increasing numbers of applications because of the features of long life, low power consumption and high reliability. The input power is increased by raising the operation current density of the LED in order to improve its brightness. As the operation current density of the LED is raised, the junction temperature is increased accordingly. Consequently, the energy band structure of the LED is changed, and the package structure or the phosphor powders in the package structure deteriorate, causing reduced brightness or performance. To improve the brightness, the thermal dissipation performance needs to be upgraded. In order to resolve the problem of high heat generated from a high power LED, many prior arts and previous studies have focuses on the significant issue of thermal dissipation.
In LED structures of the prior arts, the efficacy of the thermal dissipation is not satisfactory. For example, U.S. Pat. No. 5,563,422 puts forth that an LED die has no particular structures or apparatuses with a thermal dissipation function to assist in the heat reduction of the LED die. Accordingly, the light efficiency is generally limited.
Some of the prior arts utilize a modified electrode structure to improve the thermal dissipation of an LED die so as to resolve the problem of poor thermal dissipation. U.S. Pat. No. 6,614,172 utilizes flip chip bonding and a die with rough surface to increase the light emitting efficiency of an LED. Furthermore, electrodes with a metal structure are also used to improve thermal conduction so as to enable the LED to further have a thermal dissipation function. However, such a prior art has the problem that the electrical conduction and the thermal conduction share the same path. That is, the electrical conduction and the thermal conduction have an adverse influence on each other. Furthermore, the manufacturing yield of the aforesaid prior art is limited such that the production cost of the LED is increased.
Some of the prior arts improve the lighting efficiency of an LED by resolving the problem of poor thermal dissipation. U.S. Pat. No. 6,818,531 utilizes a laser lift-off (LLO) method to remove an LED from an original epitaxial substrate, and bonds the LED onto another substrate with good thermal conductivity so as to increase the efficiency of thermal dissipation. However, as such prior art replaces the original substrate of the LED with a thermally conductive substrate to improve the light efficiency of the LED, it needs expensive manufacturing equipment and has the disadvantages of low manufacturing yields and low productivity per unit area.
Some of the prior arts utilize a vertical type LED structure to further have the function of thermal dissipation. U.S. Pat. No. 5,739,554 also utilizes a vertical type LED structure and an N type SiC substrate to accelerate thermal dissipation. However, the cost of the N type SiC substrate is too high, its mechanical processing is poor, and its crystal quality is inferior to the crystal quality of an Al2O3 substrate. Furthermore, the SiC substrate can absorb UV light of wavelengths below 380 nm so it is not suitable to serve as a substrate carrying an LED emitting UV light with wavelengths below 380 nm.
Some of the prior arts utilize copper to cover the lateral structure of an LED for resolving the problem of poor thermal dissipation. A similar technique is disclosed by “Enhanced thermal dissipation and light output of GaN/Sapphire light-emitting diode by direct Cu electroplating,” Conference Paper National Chung Hsing University. The prior art employs copper with good thermal conductivity as the cover of the lateral structure of an LED to act as the thermal conducting interface of the LED. However, the areas of lateral side of the LED for thermal dissipation are small so the thermal dissipation effect is limited. In addition, such a structure has the aforesaid advantage of thermal dissipation only when an extra current is applied to the LED.
Some of the prior arts utilize copper to cover the lateral structure of an LED and its substrate for resolving the problem of poor thermal dissipation. A similar technique is disclosed by “Improved thermal management of GaN/Sapphire light-emitting diodes embedded in reflective heat spreaders,” Applied Physics letters 93, 11907 (2008). The prior art employs copper with good thermal conductivity to cover the substrate and the lateral structure of an LED to increase the area of thermal dissipation. The copper cover is on the substrate, however, and heat generated from the interface cannot be directly dissipated. Furthermore, the copper just covering the lateral has small dissipation areas so the thermal dissipation effect is limited.
In view of the foregoing prior arts, only the LLO technology can resolve the problem of poor thermal dissipation of the LED structure, but the other prior arts have inferior thermal conduction or are ineffective in thermal dissipation. The LLO technology has the disadvantages of high costs, low yields, and low productivity for mass production. Therefore, a new technology needs to be developed to resolve the problem of thermal dissipation of LEDs. The present invention puts forth a lateral thermal dissipation LED and a method for manufacturing such an LED. In contrast with LLO technology, the present invention has a low manufacturing cost, and can effectively resolve the problem of thermal dissipation at the interface.